1400 W MARINE VIEW DR WATERFRONT PLACE APARTMENTS Geotech Report 2022-10-25

• The evaluation of liquefaction potential is a complex procedure and is dependent on numerous site parameters, including soil grain size, soil density, site geometry, static stress, and the design ground acceleration. Typically, the liquefaction potential of a site is evaluated by comparing the cyclic stress ratio (CSR), which is the ratio of the cyclic shear stress induced by an earthquake to the initial effective overburden stress, to the cyclic resistance ratio (CRR), which is the soils resistance to liquefaction. Estimation of the CSR and the CRR were completed using both standard penetration test (SPT) and CPT based empirical methods (Youd, et al. 2001; NCHRP 2007). Estimated ground settlement resulting from earthquake-induced liquefaction was analyzed using empirical procedures based on correlations from both SPT and CPT results(Tokimatsu and Seed 1987; Ishihara and Yoshimine 1992). The results of our liquefaction analyses indicate that the very loose to medium dense sand (fill) below the design groundwater elevation is susceptible to liquefaction settlement. Our analyses suggest that the site (under existing conditions)may see free-field liquefaction-induced settlement on the order of 6 to 11 inches during the design seismic event. Differential liquefaction-induced settlements are anticipated to be on the order of 3 to 5 inches. Based on our discussions with the project team,the potentially liquefiable soils will be mitigated by means of completing ground improvement. Lateral Spreading Lateral spreading involves lateral displacement of large, surficial blocks of soil as the underlying soil layer liquefies. Lateral spreading can occur on near-level ground as blocks of surface soils are displaced relative to adjacent blocks. Lateral spreading also occurs as blocks of surface soils are displaced toward a nearby slope or free-face by movement of the underlying liquefied soil. Due to the proximity of the existing bulkhead wall (free-face) and liquefaction hazard, GeoEngineers recommends that the lateral spreading hazard be mitigated by means of ground improvement to meet the lateral deformation performance specifications presented in this report. Surface Fault Rupture Because of the thickness of the Quaternary sediments below the site,which are commonly more than about 1,000 feet thick, it is our opinion that the risk of ground rupture at the site resulting from surface faulting is low. 2015 IBC Seismic Design Information The site is classified as a Site Class F due to the presence of the liquefiable soils below the proposed buildings. However, based on collaboration with the structural engineer, it is our understanding that the building period will be less than 0.5 seconds.Consequently,the project can be completed using code-based seismic design per ASCE 7-10 and a site-specific evaluation is not required. Given that the average blowcount in the upper 100 feet is estimated to be less than 15 and the building period is less than 0.5 seconds,the site is best characterized as Site Class E, per the 2015 IBC. We recommend the use of the following 2015 IBC parameters for Site Class,short period spectral response acceleration (Ss), 1-second period spectral response acceleration (Si) and seismic coefficients(FA and Fv) 11111 for the project site (Table 1). GEOENGINEERS May31,2017 Page5 File No.22360-003-00